All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
Setting an advertisement on the taxi does not make if forbidden to work as a driver in it. Therefore, if the advertisement is for something lawful, then it is permissible for you to continue working as a driver of the taxi.
Allaah Knows best.